Crystal chemistry of cation-exchanged forms of hilairite: New experimental data and chemical composition-structure-genesis relations

摘要

The crystal structures of cation-exchanged forms of hilairite obtained at 90°C (Pb- and Rb- exchanged samples (Pb_(0.60)Na _(0.40)H_(0.40)ZrSi_3O_9 · 3H _2O [R32, a = 10.4718(3) ?, c = 7.9392(2) ?] and Rb _(1.48)Na_(0.45)H_(0.07)ZrSi_3O_9 · 0.53H_2O[R3, a = 10.4743(4) ?, c= 15.5433(8) ?]) and at 150°C (K- and Cs-exchanged samples K_(1.81)Na _(0.09)H_(0.10)ZrSi_3O_9 [R3, a = 10.3804(2) ?, c = 14.9541(6) ?] and Na_(1.14)Cs_(0.55)H _(0.31)ZrSi_3O_9 · 0.90H_2O [R32, a = 10.5472(4) ?, c = 15.8797(7) ?]) were studied by X-ray dif- fraction. Their structures are based on a framework composed of helical chains [Si_3O_9]_8 and isolated Zr octahedra. Relationships were found between the characteristics of exchange cations and the temperature of the ion exchange, on the one hand, and the compositional and structural features of the products, such as the type and degree of distortion of the framework and the concentration and arrangement of exchange cations and residual Na, and H_2O molecules, on the other hand. The affinity of hilairite for extraframework cations in the ion exchange was shown to decrease in the order K → Rb → Pb → Ba → Sr → Ca → Cs.